Highway crossing signaling system having high sensitivity to train shunts



Nov. 24, 1959 G. o. FERM ETAL 2,914,663

HIGHWAY CROSSING SIGNALING SYSTEM HAVING HIGH SENSITIVITY T0 TRAINSHUNTS Filed Feb. 24. 1956 EDT IMPULSE-4 TRANSFORMER TO XG OPERATINGAPPARATUS INVENTORS G.O.FERM AND BY M.A. SCHEG THEIR ATTORNEY HIGHWAYCROSSING SIGNALING SYSTEM HAV- ING HIGH SENSITIVITY T TRAIN .SHUNTSGlenn 0. Ferm, Gates, and Marcian A. Scheg, Rochester, N.Y., assignorsto General Railway Signal Company, Rochester, N.Y.

Application February 24, 1956, Serial No. 567,597

5 Claims. (Cl. 246-130) This invention relates to railway signalingsystems for the protection of highway crossings, and relates moreparticularly to crossing warning systems which are actuated in responseto the shunting of detector track circuits by trains.

In crossing warning systems which are operated by the shunting ofdetector track circuits, the reliability of the system is dependent uponthe sensitivity of such detector track circuits to train shunts of alltypes. The inability of track circuits to detect the presence of a traineither initially or continuously can'result in the failure of signalingoperations while trains are approaching and/or occupying the highwaycrossing. The modern use of high-speed lightweight trains raises aproblem is that the sensitivity of detector track circuits of the typeusually used in general practice is not great enough to providecontinous positive detection of such trains, since these trains providehigher wheel-to-rail contact resistance than that provided by theheavier standard trains.

A further consideration common to all crossing warning systems is thecondition of the rails of the track section which includes the highwaycrossing. Poor shunting sensitivity is common to such sections becauseof dirt, sand or other susbtances which are depositedby highway traflicand which accumulate on the rail surfaces.

In view of the preceding considerations, the present invention providesmeans for improving the operating sensitivities of detector trackcircuits, such means being applicable both to new. and to existinginstallations. More specifically, the present invention proposesithe[ICC and because of the relatively short length of standard crossingtrack sections, the installation of high voltage use of auxiliarydetector track circuits having high shunting sensitivity to cooperatewith standard approach track circuits in a manner such .that theauxiliary circuits are capable of detecting trains which might notbenormally detected by the standard approach circuits. The detectortrack circuits may be of a high voltage type or of the impulse trackcircuit type which are sensitive to highresistance train shunts. Thedetector track circuitsare used to insure the response oftheassociatedstandard approach track circuits to approaching trainsregardless.

tions.

of the ability of such trains to provide positive shunts in 1- thestandard approach track circuits. Since the track sections included insuch-detector track circuits can be relatively short in length, theaddition of detector track circuits to existing installationsisstructurally and economically feasible. f

In order to insure continuous detection of trains appreaching a highwaycrossing, the present invention further proposes the use of lock-outcircuit means to prevent the picking up of shunted or deenergizedapproach track relays until an approaching train has vacated theassociated approach track sections and has passed the highway crossing.The present invention furtherproposes the use of a high-sensitivitydetector track circuit at the highway crossing. This track circuitcan-be of the high voltage type;

ing up of the crossing track relay during intervals ofpoor shunting, orloss of shunt, until a passing train is detected as having reachedv theexit side of the crossing section.

In using detector track sections in advance of approach track sections,conditions can arise in which a train may completely pass the crossing,but fail toshunt theapproach track circuit at the leaving end. Duringtime 'intervals when the approachtrack section alone is occupied,

a momentary loss of shunt could result in the clearing out of thewarning circuits, followed by the reactivation of the circuits when ashunt is reestablished. Under such. conditions, warning signals could beleft in operation after the departure of the train. To preclude theresponse of approach track relays to momentary los'ses'of shunt, thepldsfillt invention includes circuit means for rendering the approachtrack relays non-responsive to energies which would normally energizesuch track relays whenever the detected train is receding fromthehighway crossing. The pick-up characteristics of the approach trackrelays are, in other words, rendered selective-' ly sensitive to themagnitude of operating voltages, and such selections are made throughthe use of directional stick relays. More specifically, it is proposedthat directional stick relays which are selectively energizedto-indicate directionsof train movement be used to qualify the pick-upcircuits for the approach track relays" ina manner such that an approachtrack relay is rendered responsive to normal energization when a trainis approaching the crossing through the approach track section and isrendered responsiveonly to a higher level of energization when anoccupying train is receding from the crossmg. I I v Since interdependentlock-out circuits are proposed for both the crossing and approach trackrelays, means must be provided .to prevent the mutual locking out ofsuch track relays under abnormal 'op'erating conditions.- The presentinvention includes timing relay means which is actuated in response tothedetection 10f an approach' ing train. The timing means is capable ofmeasuring a time interval which is normally suflicient for a train tocompletely pass through the various detector track sec Upon thecompletion of a timing operation; circuit means are established-topermit the restoration of the crossing and approach track relays totheir normal energized states, provided that such relays are not shuntedin any manner. I f

In view of the preceding considerations, an object of this invention isto provide auxiliary detector track cir cuit means having high shuntingsensitivity for insuring the detection of trains approaching a highwaycrossing. Another object of this invention is to provide lock-outcircuit means for preventing the picking up of shunted approach wtrackrelays whenever the associated approach track circuit means having highshunting sensitivity and including lock-out circuit means responsivetooperations of the approach track circuits forpreventing the picking upof the crossing track relay whilethe crossingrtr'ack section is occupiedby trains which produce poor shunts;

A further object of this invention is to provide tint Patented Nov. 24,1959,

In addition to irnproving means for restoring the various approach andcrossing track circuits to their normal states whenever abnormalconditions occur which might result in the locking up the track circuit.system. Y

Other objects, purposes and characteristic features of the presentinvention will be in part obvious from the accompanying. drawings, andin part pointed. out as the description of the invention progresses.

For the purpose of simplifying the illustration and facilitating in the.explanation, the various parts and circuits constituting the embodimentof the invention have been shown diagrammatically and certainconventional illustrations; have been employed, the drawings having beenmade more with the purpose of making it easy to understand theprinciples and mode of operation, than with the idea of illustrating thespecific construction and arrangement of parts that would be employed inpractice. Thus, the various relays and their contacts are illustrated ina conventional manner, and symbols are used to indicate connections tothe terminals of batteries, or other sources of electric current,instead of showing all of the wiring connections to these terminals.

The symbols (-1-) and are employed to indicate the positive and negativeterminals, respectively, of suitable batteries or other sources ofdirect current, and the circuits with which these symbols are usedalways have current flowing in the same direction.

Apparatus In the accompanying drawings, a stretch of railway track isshown intersected by a highway H. The stretch of track is dividedinto acentral or crossing track section XT, two approach track sections ET andWT, and two approach detector track sections EDT and WDT. The varioustrack sections are electrically insulated from each other by insulatedjoints 4. Crossing. warning protection is given by warning signals XGwhich are located on each side ofthe stretch of trackalong the highwayH.

The west approach. detector track section WDT is included in a trackcircuit comprising a battery 8, a relay WDTR and two variable limitingresistors 9 and. 10. The winding of relay WDTR. is connected to one railthrough either its stick contact 11 or front contact 12 of a repeaterrelay WDTBP. Thus, relay WDTR is actually a stick relay for reasons tobedescribed later. The track circuit is a high voltage circuit, in thatthe voltage applied to the rails by the battery 8 is of a greatermagnitude than that normally supplied for ordinary types of trackcircuits. The track circuit is adjusted by the resistors V 9 and in theusual manner to provide a track circuit shunting sensitivity which ishigh enough to detect lightweight trains which'provide high-resistanceshunts.

g The east approach detector track section EDT has an associated trackcircuit which is shown to be of the impulse type. A track circuit ofthis type is described in detail in the co-pending application Ser. No.454,956 of M. A. Scheg, dated September 9, 1954, now U.S. Patent2,859,335, granted November 4, 1958; and relying on that application fora complete description of track circuit operations, the presentdescription will be confined to former, and the directions of magneticflux produced by current in the two windings are in opposition. When thetrack circuit is shunted by a train, the winding 20 of the impulsetransformer is shunted, while the current produced by the train shuntrises sharply in the winding 14 of the impulse transformer. Theresulting change in magnetic flux induces a voltage across a secondarywinding 20, and this induced voltage is applied to the winding of theimpulse relay IR through rectifiers 21 and 21a. Relay IR is assumed tobe a polar relay, and it can be noted that one terminal of the windingof the relay IR is connected to a center tap provided in the winding 20,while the other terminal of the relay winding is connected through therectifiers 21 and 21a to the extremities of the Winding 20. In thismanner, relay IR is energized by energy of a particular polarityregardless of the polarities of voltage induced in the secondary windingof the transformer. A capacitor 22 can be connected across the secondarywinding 20 to reduce the effects of initial sharp peaks of inducedvoltage applied across either rectifier, thereby protecting therectifiers against inverse voltages.

When relay IR is energized by a pulse of induced voltage, it isdesirable to maintain the picked-up condition of the relay for a timeinterval sufiicient to operate a repeater relay EDTP. Therefore,slow-release characteristies are provided in the present disclosure bymeans of a resistor-capacitor unit 23 connected in parallel with thewinding of relay IR.

Under ideal shunting conditions, the occupancy of the track section EDTresults in the deenergization of the track relay EDTR and the concurrentenergization of the impulse relay IR. Back contact 24 of relay IR andfront contact 25 of relay EDTR both open to deenergize a repeater relayEDTP. relay EDTP is deenergized either by a normal shunt across thetrack rails or by a momentary detected shunt which results in theoperation of the impulse track relay. Relay EDTP is normally energizedthrough its stick contact 26, and can also be energized through frontcontact 27 of a repeater relay EDTBP, The function of the two energizingcircuits will be described later in detail;

The track repeater relay EDTP cannot be energized until the impulserelay IR is again actuated to close its front contact 17 to pick uprelay EDTR. Since this cannot occur until an occupying train vacates thetrack section EDT, relay EDTP will remain deeuergized, thereby detectingtrack occupancy conditions. The description of an impulse track circuitis given primarily to illustrate analternate means for detecting poorshunting cars. Inactual practice either a high-volt age track circuit ofthe type described for the west approach detector track "section WDT oran impulse track circuit can be used, but the type of track circuit tobe used need not be limited to the two examples shown.

Each of the approachdetector track relays-WDTR and EDTP have slow-actingback repeater relays WDTBP and EDTBP, respectively. Back contacts 28 and29 of a general description of the circuit elements and theiroperations. The track circuit apparatus includes a battery 13 and alimiting resistor 13a which are connected to the rails of the tracksection through a Winding 14 V of an impulse transformer. A trackrelay'EDTR is connected to the rails at the other end of the tracksection by a circuit which can be traced from the upper rail throughwire 15, either front contact 16 of relay EDTR or front contact 17 of animpulse relay IR, the winding of relay EDTR and a wire 18 to. the lower,rail. A second winding 19 of the impulse transformer is connected inparallel with the winding of relay EDTR. When the track section isunoccupied,.current flows. from the battery through the windings. 14.and. 19 of the impulse transrelay WDTR and-EDTP, respectively, act toenergize or deenergizethe associated back repeater relays.

The high-voltage detectortrack circuits are used to insure the responseof trackcircuits associated with the track sectionsW'I and ET topoor-shunting trains. In the present disclosure, this is accomplished byopening the track circuits associated with the approach track sectionsat the battery ends. More specifically, under normal conditions theapproach tracksection WT is energized by a battery 30 which is connectedat one terminal to the lower. rail by a wire.31 andis connected at theother terminalto the upper rail by a circuit including front contact 32ofirelay WDTRand two resistors 33 and 34. It is evident that a shuntingof relay WDTR results in the disconnecting of the battery 30 from therails by the opening of front contact 32 ofrelay WDTR. A second circuitfor. applyingenergy: tothe rails of track section In this manner, the

includes the battery 30 and a second battery'36 which can be connectedto the rails through front contact 37 of relay WDTBP, front contact 38of relay WDTR, and

the resistor 34. This circuit is effective momentarily when a trainvacates the track section WDT to cause the energization of relay WDTRwhich closes its front contact 38 before the slow-acting repeater relayWDTPB can releaseits front contact 37. This operation will be describedlater in greater detail.

It can be seen that a similar energizing circuit is associated with theapproach track section ET, and it is con trolled by the relays EDTP andEDTBP.

The track circuit associated with the approach track section WT includesa track relay WTR which is normally connected to the rails of the tracksection through a resistor 39, front contact 40 of relay WTR, and'a wire41. Obviously; the circuit described for energizing relay WTR is a stickcircuit. Therefore, relay WTR when deenergized must be dependent onparticular pick-up circuit means for restoring the relay to itspicked-up condition.

WTR whenever the track section WT is vacated. One pick-up circuitincludes the resistor 39, a resistor 42, front contact 43 of adirectional stick relay WBS, front contact 44 of thecrossing track relayXTR, and wire- 41. The remaining two pick-up circuitsboth include frontcontact 44 of relay XTR and include, respectively, front contact 45 of atiming repeater relay TESP and front contact 46 of a directional stickrelay EBS. Without describing the various pick-up circuits'specifically,it can be noted that relay WTR can be energized only when the crossingtrack relay XTR is energized and either directional stick or timingcircuit means are operated.

The approach track relay ETR is provided with similar pick-up and stickcircuit means. The stick circuit for relay ETR includes a resistor 47,front contact 48 of relay ETR and a wire 48a. The pick-up circuits forrelay ETR all include front contact 49 of the crossing relay XT R, andthe respective pick-up circuits include, respectively, front contact Silof relay WBS, front contact 51 of relay TESP, and front contact 52 ofrelay EBS which is connected in series with a resistor 53. e

' The crossing track section XI has an associated track circuit which isenergized by a battery 54 through a limit-' ing resistor 55. The battery54 is a high-volta-ge source comparable to those described for thedetector track sections. The crossing track relay XTR is normallyenergized through a stick circuit which includes a limiting resistor 56and a front contact 57 of relay XTR. -Relay XTR is provided with aplurality of pick-up circuits; One pick-up circuit arrangement includescontacts 58 and 59 of the respective approach track relays ETR and WTR,while the remaining pick-up circuit includesfront contact 60 of thetiming repeater relay -T ESP. It is evidentthat pick-up operations ofrelay XTR are possible only'in response to operations of the approachtrack relays orto the completion of timing operations which will bedescribed. The high-sensitivity track circuits employed in conjunctionwith the track sections XT and WT are, as described, of a type in whichthe supply voltage is higher than that normally employed in trackcircuits in general. Shunting resistance is dependent on thewheel-to-rail contact resistance encountered, and often such resistanceis jhigh because of the condition of the Wheel and rail surfaces. Oftensuch high contactresistance is caused by surface layers of dirt, grease,etc. A higher interrail potential is one effective means for overcomingthe contact resist ance and, thereby, increasing the effectiveness of ashunt.

Two directional stick relays EBS and WBS are provided to indicate thedirections of movementof trains passing through the stretch of track.The eastbound directional stick relay EBS has a pick-up circuit whichincludes'back contact 61 of relay WTR, back contact 62. of relay XT R,front contact 63 of relay ETR, back contact 64 of relay A plurality ofpick-up circuits are provided for restoring relay' W38, and the windingof relay EBS. Stick circuits for relay EBS are provided through itsstick contact 65 and either back contact 63 of relay ETR or backcontacts 61 and 62 of relays WTR and XTR, respectively. The pickupcircuit for the westbound directional stick relay WBS includes backcontact 63 of relay ETR, back contact 62v of relay XTR, front contact 61of relay WTR, back contact 66 of relay EBS and the winding of relay WBS.Relay WBS can be energized by stick circuits which in-' clude its frontcontact 67 and either back contact 61.of

relay WTR or back contacts 62 and 63, respectively, of

relays XTR'and ETR. -Without describing the operation of the directionalstick relays in detail, it can be noted that a particular directionalstick relay is energized whenever an approach track relay and thecrossing track relay are concurrently deenergized, and energization ismaintained until a train causing such pick-up operations vaby a circuitincluding front contacts 68, 69 and 70 of' relays WTR, XT R, and ETR,respectively. From this it can be seen that initially relay XR can bedeenergized by the shunting of any of the approach and crossing trackcircuits. Front contacts 71 and 72 of the directional stick relays WBSand E88, respectively, are provided inthe pick-up circuit for relay XRto operate relay XR" under particular conditions of track occupancywhich will be described. Whenever relay XR is deenergized, it closes itsback'contact 73 to energize the operating circuits (not shown) for thecrossing warning signals X6; and itlis' assumed that such controlcircuits can be of any of a number of well-known types.

In order to provide circuit means for restoring the various trackcircuits to normal under unusual operating conditions, a timing relay TEis provided. Although the timing relay can be of any of a number oftypes, it is assumed in the present disclosure that relay TE is of awell-known thermal type. More specifically, relay TE is assumed'toinclude a bimetallic contact member which is caused to bend inaccordancewith temperature. This Well-known type of contact member ismade of two attached strips of dissimilar metals which have differentthermal coefficients of expansion. Thus, under varying conditions ofheating the metallic strips expand or con: tract at different'ratescausing the contact member to bend. In the circuit drawing thebimetallic contact mem-' her is shown as a front contact 77 which islocated in close proximity to the relay Winding, or heating element.Contact 77 is assumed to be fully open when the winding isdeenergized,and is assumed to'bend to its closed positions in response to heatproduced in the relay winding when energy is applied to the winding. Acheck contact The timing relay TE can be energized by'a circuitiricluding either back contact 74 of relay [WTR or back contact 75 ofrelay ETR, the winding of relay TE, and back contact 76 of a stick relayTES. 'Thus,-when an approach track section ET or WT is occupied energyis applied to relay TE, and the resulting heat produced in the windingof relay TE causes contact 77 to 'move toward its closed position. Thismovement of contact 77 causes contact 79 to move from its closedposition at the same time. V j Q The stick relay TES is providedtodetect operations of relay TE which result in the closing of contact77 of relay TE. When relay TE is energized for a time interval longenough to result in the closingof contact 77, relay TES becomesenergized by a circuit including either back contact 74 or 75 of relaysWTR and ETR, respectively, contact 77 of relay TE, the winding of relayTES and back contact 78 of a repeater relay TESP. When relay TES opensits back. contact 76 and closes its front contact 76"relay TEismomenta'rily deenergized. Front contact 76 establishes an alternateenergizing circuit for relay TE and establishes a stick circuit forrelay TES. While front contacts 76 and. 77 of the respective relays TESand. TE are both closed the winding of relay TE is shunted, and thisshunt circuit combination is in series with the winding of relay TES.Thus, the current in relay winding TE decreases, and the heat producedby the winding of relay TE decreases accordingly, resulting in theopening of contact 77. When contact 77 of relay TE opens, the windingsof relays TE and TES are connected inseries through front contact 76 ofrelay TES.

' The resistance of the winding of relay TES, however, is

high enough to maintain the level of current low in this series circuitso that insufiicient heat is produced by the winding of relay TE toaffect contact 77, and contact 77 moves to its fully open normalposition, while contact 79 of relay TE moves to its normally closedposition.

In view of the operation of the relays TE and TES, a timing operationbegins with the energization of relay TE and ends with the reclosing ofback contact 79 of relay TE. When back contact 79 closes, the repeaterrelay TESP is energized by a circuit including front contact 80 of relayTES. Relay T ESP opens its back contact 78 in the energizing circuitsfor relay TES, causing relay TES tobe deenergized. In order to insurethat the pick-up circuit for relay TESP is closed long enough to causethe relay to pick up its armature relay TES is made slow-acting inreleasing its armature, as previously described. When relay TES releasesits armature, front contact 80 of relay TES then opens to deenergizerelay TESP. Thus, relay TESP is energized momentarily at the end of eachtiming operation and causes the deenergization of relay TES. If eithercontact 74 of relay WTR or contact 75 of relay E'ER is closed at the endof one timing operation, the closing. of back contact 76 of relay TEScloses the previously described initial energizing circuit for relay TEto start another timing operation.

Relay TESP, during periods of energization, acts in the previouslydescribed pick-up circuits for the approach and crossing track relays.The function of the relay TESP in establishing pick-up circuits forthese track relays can best be described when a more specificdescription of circuit operation is given. It should be noted that relayTESP is made slow-acting in releasing its armature so that contacts ofrelay TESP in approach and crossing track circuits are closed longenough to per mit circuit operations.

Operation In. describing the operation of the present circuits itinitially and described later.

7 It will be assumed that. an eastbound train advances into and throughthe stretch of track, and it is assumed that the length of the train issuch that all of the track sections can be occupied by the train at onetime.

When the train enters the west approach detector track section WDT ashunt is produced in the associated detector track circuit. Since, asdescribed, the approach detector. track circuit is. of a high voltagetype, adjusted to be responsive to high-resistance shunts, the range ofshunt detection. is greater than the range of standard track circuitsencountered in general practice. Therefore, even under poorshuntingconditions the detector track, circuit. can be expected. torespond, at least momentarily, to a train shunt. Thus, relay WDTR isshunted and releases its armature, resulting in the opening of frontcontacts 11, 32 and 38 and the subsequent closing of back contact 28.

The opening of front contact 32 of relay WDTR deenergizes the westapproach track relay WTR, since front contact 32 of relay WDTRdisconnects one terminal of the battery 30 from the upper rail of theapproach track section WT. Since relay WTR is normally energized by astick circuit including its front contact 40, relay WTR cannot bereenergized until energy is again supplied to the rails and until one ofthe previously described pick-up circuits closes. Thus, any effectiveshunting of relay WDTR results in the deenergization of the approachtrack relay WTR, and the continued deenergization of relay WTR is notdependent upon the ability of a train to produce effective shunts in theapproach track section WT.

In addition to disconnecting the battery 30 from the track section WT,relay WDTR also precludes the connecting of the batteries 30 and 36, inseries, to the track rails. Specifically, front contact 38 of relay WDTRis open before front contact 37 of the repeater relay WDTBP closes inresponse to the energization of relay WDTBP by the closing of backcontact 28 of relay WDTR.

It should be noted here that whenever relay WDTR is again energized itopens its back contact 28 to deenergize relay WDTBP. Since relay WDTBPis slow-acting in releasing its armature, front contacts 32 and 38 ofrelay WDTR close before front contact 37 of relay WDTBP opens. Thus, fora moment the batteries 30 and 36 are connected in series in the trackcircuit associated with the approach track section WT, and a pulse ofhigher voltage is, applied to this track circuit momentarily. However,no pick-up circuit is closed at this time to permit relay WTR to respondto the high voltage pulse. The utility of the application of a highvoltage pulse is particularly related to operations resulting fromtrains leaving the stretch of track and will be further described later.

When the train advances into the approach track section WT, no furthercircuit operations occur because relay WTR is already deenergized. Itmust be noted at this time that the approach track circuit includingrelay WTR is a standard track circuit, responsive to train shuntsfalling within a normal range of resistance. This track circuit can bereasonably assumed to be responsive, at least momentarily, to poorshunts. Therefore, even a momentary effective shunt which can bedetected by the approach track circuit results in the sustained deenergization of relay WTR until a pick-up circuit is closed for thatrelay. The combination of the approach track circuit and the adjoininghigh-sensitivity approach detector track circuit thereby insures thedeenergization of the approach track relay WTR as an eastbound trainenters the stretch of track.

The deenergization of relay WTR results in the opening of front contact68 of relay WTR in the normal energizing circuit for the crossing relayXR. Relay XR releases its armature and closes its back contact 73,thereby activating the operating apparatus for the crossing warningsignals XG.

When the train advances into the crossing track section XT the trainshunt produced in the crossing track circuit results in thedeenergization of relay XTR. Since this track circuit is also of thehigh-voltage type, adjusted to respond to high-resistance train shunts,the susceptibility of relay XT R to shunting is high. The detection ofeven a momentary shunt by relay XT R is sufiicient to sustain thedeenergization of the relay because relay XTR is normally energizedthrough its stick contact 57. Thus, one of the pick-up circuits forrelay XTR must be closed before the relay can again be energized.

The deenergizationof relay XTR results in. the energization of theeastbound directional stick relay EBS through the pick-up circuitincluding back contact 61 of relay WTR, back contact 62 of relay XTR,front contact 63 of relay ETR, and back contact 64 of relay WBS. A stickcircuit including back contacts 61 and 62 of relays WTR and XTR,respectively, and front contact 65 of relay EBS then closes to holdrelay EBS energized.

' As the train advances into approach track section ET it may or may notbe capable of effectively shunting relay ETR. If relay ETR is shunted,at least momentarily, it will openits stick contact 48 and becomedependent on its pick-up circuits for subsequent reenergization. If thetraincannot efiectively shunt relay ETR, the subsequent entrance of thetrain into the approach detector track section EDT can be expected toresult in the deenergization of relays EDTP and ETR. More specifically,the combination of track circuits associated with track sections ET andEDT is comparable to that associated with track sections WT and WDT.Although, for illustration ofalternate types of high-sensitivity trackcircuits, thetrack circuit for track section EDT has been assumed to beof the impulse type, operations of this track circuit result inoperations of relay EDTP which selectively connect or disconnect trackbatteries in the track circuit for track section ET.

Assuming that the train is capable of shunting relay ETR, at leastmomentarily, relay ETR releases its armature; The crossing over of themovable contact spring of contact 63 of relay ETR opens the pick-upcircuit for relay EBS and subsequently closes to provide another stickcircuit for relay EBS.

l Assuming at this point that all of. the track sections are :occupiedby the train, the condition of the various track circuits should bereviewed. Relays WDTR, XTR andEDTR are deenergized because of the.shunting action of the train. Relays WTR andETR are deenergized,regardless of effective shunting, because their respecti"e pick-upcircuits are opened by front contacts 44 and 49, respectively, of relayXTR; and furthermore, their respective energy supply batteries aredisconnected by contacts of relays WDTR and EDTP, respectively.

9 When the train vacates track section WDT, relay WDTR picks up, closingits front contacts 32 and 38 to apply high voltage to the rails of tracksection -WT, as previously described, through front contact 37 of theslow-release'WDTBP. When relay WDTBP opens its front contact 37, theenergy supplied to track section WT reverts to normal, being supplied bybattery 30 through front contact 32. of relay WDTR. Relay WTR cannot,however, be picked up until the train vacates track sections WT and XT.As soon as'track section XT is vacated, removing the train shunt fromrelay XTR, relay XTRis energized through back contacts 58 and 59 ofrelays'ETR and WTR, respectively. Stick contact 57 of relay XTR closesto restore the normal "energizing circuit .for relay XTR. Relay WTRbecomes energized as soon as front contact 44 of relay XTR closes. Thepick-up circuit efifective at this time includes front contact 46 ofrelay EBS as well asfront contact 44 of relay XTR. The normal energizingcircuit for relay WTR: is' closed by the stick contact 40,,of relay WTR;

,nA pick-up circuit for relay XR is now closed through front-contacts68, 69 and 72' of relays WTR, XT R and BBS, respectively. Relay XR picksup and opens its back contact 73, thereby stopping operations of thewarnsignalsXG. Thus, signaling operations cease when the. train vacatesthe crossing. I I

When the train vacates track section ET, no circuit ll rations occur.When track section EDT is vacated, i removal ofthe shunt produces 'apulse of energy in the secondary winding of the impulse transformer, aspreviously described, resulting in the momentary energizationof theimpulse relay IR. The closing pr. front contact 17 of relay IR permitsthe picking up of the track 10 relay EDTR which, in turn, closes itsstick contact 16 to restore its normal energizing circuit. The repeaterrelay EDTP is then energized as soon as the impulse relay IR releasesits armature to close back contact 24. The slow-acting repeater relayEDTBP is deenergized, but retains its armature long enough to permit themomentaryapplication of a pulse of high-voltage energy to the rails oftrack section ET. This results in the pickingup of relay ETR through itspick-up circuit including front contact 49 of relay XTR, front contact52 of relay EBS and the resistor 53. Relay ETR closes its stick contact48 and is maintained energized by its normal energy supply battery afterrelay EDTBP releases to cut off the highvoltage pulse.

The picking up of relay ETR results in the opening of the stick circuitfor relay EBS at back contact 63 of relay' ETR. The deenergization ofrelay EBS returns'the circuits to their normal operating status.v It canbe noted here that relay EBS (and W138) is of the slow-release type toinsure the continuous energization of relay XR. Specifically, frontcontact 72 of relay EBS must remain closedunt'il'front contact 70 ofrelay ETR closes; otherwise' momentary undesirable operations of thecrossing signals could result.

Returning to the conditions under which relay ETR became energized whenthe train vacated the detector track section EDT, the pick-up circuitavailable for energizing relay ETR included the resistor 53.This'resistor is adjusted to be capable of preventing the picking up ofrelay ETR by normal energization, but permits the pick-' ing up'of relayETR in response to the momentary pulse of high-voltage energy producedwhen track section EDT is vacated. Theutility of this circuitarrangement can be seen in considering conditions underwhich a shorteastbound train advances into the track section ET and is' completelycontained within the limits of that track section. The condition of thecircuits under such conditions is dependent upon whether or not-thetrain is, or has been, capable of effectively shunting relay ETR. Sincerelay WTR- cannot be picked up until relayXTR picks up, and since relayXTR cannot pick up unless both relays WTR and ETR are dropped away, theclear ingup of the track circuits previously shunted by the train isdependent upon the deenergization of relay ETR. Assuming that the traindoes effectively shunt relay ETR, relay ETR drops awaypermitting theenergization of relaysXTR and WTRin sequence. A pick-up circuit is nowavailable for relay'ET-R and includes the resistor 53along with frontcontacts 52 and 49 of therespective relays -EBS and XI R. If the shuntproduced by the train should become poor,-or lost completely, relay ETRwill not be picked up by its normal energy supply which is availableWhenever track section EDT is unoccupied.

. If such operations were permitted, a momentary; loss of shunt couldcause r'elay ETR to pickup, resulting-in the deenergization-of relay EBSiwhichj'at this point, vis held energized by itsstickcircuit throughback contact 63 of relay-ETR. Asubsequentdeenergization of relay ETR;upon a reestablishing of the effective train shunt would result in, thedeenergization of relay -XR; specifically; front contact 17 0" of relayETR and front contact'72 of relay BBS would open the, energizingcircuits for relay XR. 'Thus', the momentary loss of shunt could causethe reactivation of the warning signals XG, and signaling ofhigh-voltage energy in the pick-up" circuit for relay- ETR.

In view of the foregoing description, it can be pointed out that duringthe time when relay ETR can be'energizedby high-voltage energy throughthe biasing resistor 53, the approach track circuit is essentially ahigh-voltage circuit comparable to those associated with track sectionsWDT and XT; and this circuit is arranged to be sensitive tohigh-resistance shunts. Therefore, if the front of a train shouldproduce an effective shunt followed by a momentary loss of shunt whenentering track section EDT from track section ET, relay ETR is notresponsive to the resulting high-voltage energy pulse because relay ETRis etfectively connected into a circuit having high shunting sensitivityat the time, and the shunt produced by the remainder of the train intrack section ET will be detected.

A westbound train moving through the stretch of track will producesimilar circuit operations. The track relays EDTP and ETR are droppedaway in sequence, and warning signaling operations are initiated by theopening of front contact 70 of relay ETR in the energizing circuit forrelay XR. The subsequent shunting of relay XTR results in theenergization of the westbound directional stick relay WBS which, inturn, conditions the pickup circuits for relays ETR and WTR. The latershunting of relay WTR conditions the pick-up circuit for relay XTR sothat relay XTR will pick up when the train vacates track section XT. Atthis time relay ETR can be energized by its normal energy source throughfront contact 50 of relay WBS, while relay WTR can be energized only byhigh-voltage energy through the biasing resistor 42 and front contact 43of relay WBS. As previously pointed out, the biasing resistors 42 and 53are selectively inserted in the pick-up circuits for re lays WTR andETR, respectively, in order to prevent energizations of relays WTR andETR which result from losses of shunt. Since the biasing resistors areeither inserted or by-passed by selective operations of the directionalstick relays EBS and WBS, it is essential that concurrent energizationsof relays EBS and WBS be prevented. Thus, as described, the pick-upcircuit for relay EBS includes back contact 64 of relay WBS, while backcontact 66 of relay EBS is included in the pick-up circuit for relayWBS. This cross-checking in the pick-up circuits for relays EBS and WBSinsures the prevention of concurrent energizations of these relays underany-conditions which might conceivably arise.

Having described circuit operations resulting from the passing of atrain through the stretch of track, various specific operating featurescan be pointed out in detail.

The arrangement of the approach detector track sections and approachtrack sections is such that a train entering the stretch of track isrequired to produce at' able of deenergizing either relay WDTR or WTR,and

such a shunt will cause relay WTR to drop away and initiate warningsignaling operations. Since relay WTR is normally energized by a stickcircuit it cannot be again picked up until a pick-up circuit is closed.Excluding the timing means, no pick-up circuit is available to relay WTRuntil the directional stick relay EBS is energized; and no directionalstick relay can be energized until the crossing track relay XTRis'effectively shunted. Therefore, the system will cause safe conditionsto prevail even if the eastbound train does not produce a singleeffective shunt in passing through track sections XT, ET and EDT. Unlessrelay XTR is shunted, relay EBS cannot be picked up; and unless relayEBS picks up in response to the eastbound train, relay WTR cannot have aclosed pick-up circuit. Similarly, a westbound train which effectivelyoperates the impulse track circuit or shunts relay ETR, causes thedeenergization of relay ETR, re-

'dition especially when visibility is poor.

The arrangement of the track circuit associated with the crossing tracksection has particular utility in the present system. As previouslydescribed, relay XTR is normally energized by a stick circuit. Oncedeenergized, relay XTR cannot be picked up again until both of the trackrelays ETR and WTR are either energized or deenergized (ex eludingtiming circuit operations). If the crossing track circuit were arrangedto be similar to that associated with track section WDT, the possibilitywould arise that a short train, engine, or railway car could shunt relayXTR when occupying only the extremities of the track section. In otherwords, deposits accumulated on the rail surfaces at the highway couldprevent effective shunting in the highway sector. Thus, 'an eastboundtrain could produce an effective shunt upon entering the crossing tracksection, but would fail to shunt upon entering the highway sector. Ifthe crossing track relay XTR were capable of responding to suchoperations, and since track section WT would have been vacated, relayXTR would first drop away causing relay EBS to pick up. Relay WTR couldthen pick up when relay XT R is picked up in response to the loss ofshunt. The crossing relay XR would then be energized, causing thecessation of warning signaling operations. Thus, a short train, engineor railway car could occupy the crossing undetected, this being anunsafe con- On the other hand, if the short train proceeded through thecrossing, again shunting relay XTR at the east end of the crossing tracksection, the warning signaling operations would be again initiated. .Thepresent circuit arrangement preeludes the assumed unsafe cessation ofwarning signal operations because if relay XTR is once shunted it cannotpick up again until the train is detected by the dropping away of relayETR. Thus, relay WTR is held deenergized by relay XTR, and relay XTR isheld deenergized by relay ETR until relay ETR becomes deenergized.Obviously, if the train has advanced far enough to shunt relay ETR itmust also occupy an extremity of track section XT where shuntingconditions are good.

' In view of the preceding, the approach and crossing track circuits arearranged to cooperate so that lock-out means are provided to preventunsafe energizations of the associated track relays under conditions ofpoor shunting;

As stated earlier, the west approach detector track circuit is arrangedso that the associated track relay WDTR is normally energized throughits stick contact 11 and can be picked up only when front contact 12 ofthe associated repeater relay WDTBP is closed. Relay WDTBP is energizedwhen relay WDTR is deenergized, closing back contact 28. It is essentialthat relay WDTBP be picked up in response to the shunting of relay WDTRso that front contacts 38 and 37, respectively, of relays WDTR and WDTBPare closed for an interval to deliver a' high voltage energy pulse forrestoring the approach track relay WTR. If the picking up of relay WDTRwere not dependent uponthe picked up condition of relay WDTBP conditionscould arise wherein a brief shunting of relay WDTR might not'result inthe energizationof relay WDTBP, and such brief shunting intervals canexist when a short train (or a single car) passes through thetrack'section WDT at a high speed. Thus, the present circuitarrangements enforces a complete cycle of operation by relay WDTR andWDTBP in response to any effective shunting of relay WDTR.

. Similarly, the relays EDTP and EDTBP associated with the east approachdetector track section are operatedin a like manner, relay EDTP beingnormally energized by'a stick circuit and being subjected to pick upenergization only if relay EDTBP is energized.

Attention can now be given to the function of the tim ingcircuit means.As described previously, the thermal element of the timing'relay TE isenergized whenever an approachtrack relay WTR or'ETR is deenergized..The subsequent heating causes 'back' contact 79 of relayTE to' open andcauses 'front"conta'ct"77 of relay TE to close. Relay TES is energizedwhen contact 77 of relay TE closes, and the subsequent alteration of thecircuit arrangement results in both the shunting of the heating elementand the addition of the winding of relay TES in series with the shuntedheating element. The resulting cooling causes contact 77 of relay TE toopen. Subsequently, back contact 79 of relay TE closes to energize relayTESP, and back contact 78 of relay TESP opens to deenergize relay TES.The deenergization of relay TES results in the deenergization of relayTESP by the opening of front contact 80 of relay TES. When back contact76 of relay TES again closes, the timing operation can be repeated ifone or the other (or both) of the approach track relays WTR and ETR isdeenergized.

The timing cycle is adjusted to be slightly longer in duration than thetime normally required for a train to pass completely through thestretch of track at a normal speed.

Whenever relay TESP is picked up, its front contacts 45 and 51 close inpick-up circuits for relays WTR and ETR, respectively, thereby renderingthese relays dependent only on the condition of the crossing track relayXT R. The conditions of the directional stick relays EBS and WBS arethereby rendered immaterial to the picking up of relays WTR and ETR.Front contact 60 of relay TESP provides a pick-up circuit for relay XTRwhich excludes contact of the approach track relays ETR and WTR. Sincerelay TESP is energized only briefly at the end of each timing cycle, itis made slow-acting so that its front contacts are closed long enough topermit operations of the track relays.

Assume that an eastboun". train enters the stretch of track and causesthe deenergization of relay WTR. Assume further that before reaching thecrossing track section XT the train stops, reverses its direction ofmovement, and leaves the stretch of track. The deenergization of relayWTR causes the deenergization of relay XR and the energization of thetiming relay TE. Warning signal and timing operations are therebyinitiated and continue as long as relay WTR is deenergized. Thedeparture of the train cannot cause relay WTR to pick up because nopick-up circuit is closed. When the timing operation progresses farenough to cause the energization of relay TESP, however, front contact45 of relay TESP closes to establish a pick-up circuit for relay WTR.The resulting picking up of relay WTR restores the circuits to normal,cutting oif signaling and timing operations.

If an eastbound train advances into the crossing section XT beforereversing its direction of movement and departing from the stretch oftrack, timing and signaling operations are efiected as soon as relay WTRdrops away. Since relay XTR is also assumed to drop away, relay EBS isenergized to close its contact 46 in one pick-up circuit for relay WTR.However, neither relay XTR nor WTR can be energized when the traindeparts. Relay XTR cannot be picked up because back contact 59 of relayWTR is closed while back contact 58 of relay ETR is not closed; andwhile relay XTR is deenergized the pick-up circuits for relay WTR areopened by front contact 44 of relay XTR. Relays XTR and WTR are therebymutually locked out. When relay TESP becomes energized near the end of atiming cycle, its front contacts 45 and 60 close in pickup circuits forrelays WTR and XTR, respectively. Relay XTR picks up, closing its frontcontact 44 in the pick-up circuits for relay WTR, .and the opening ofback contact 62 of relay XTR deenergizes relay EBS. If the train hasvacated track sections WT and WDT before relays TESP and/or EBS releasetheir 14 armatures, the closing of frontcontact 44 of relay XTR willpick up relay WTR; otherwise relay WT R will remain deenergized andinitiate another timing cycle. Timing cycles will be repeated untilrelay WTR can be picked up.

Similar conditions to those described above for trains reversingdirections of movement ,canjbe'produced by accidental shunts or opencircuits which cause either the deenergization of relay WTR or thedeenergization of relays WTR and XTR. It is further evident that similaroperations result from comparable deenergizations of either relay ETR orrelays ETR and XTR.

In view of all of the preceding descriptions of circuit operations, itis evident that the present invention provides highway crossingprotection means having a high integrity of operation. The presentsystem offers improved means for insuring both the detection of trainsand the safe operation of warning signaling means when such trains areincapable of producing continuous effective shuntings of the varioustrack circuits.

Since the problem of track circuit operation in response to poor shuntsis not confined by any means to highway crossing systems, the circuitarrangements disclosed herein have general utility in other signalingsystems as well.

Having described a highway crossing signaling system as one specificembodiment of the present invention, it is desired to be understood thatthis form is selected to facilitate in the disclosure of the inventionrather than to limit the number of forms which it may assume; and, it isto be further understood that various modifications, adaptations andalterationsmay be applied to the specific form shown to meet therequirements of practice, without in any manner departing from thespirit or scope of the present invention.

What we claim is:

1. A control system comprising a highway crossing signal, a stretch ofrailway track extending across a highway, crossing means for registeringthe presence of a train in a short section of track traversed by thehighway, intermediate approach means for registering the presence of atrain on approach sections of track adjacent to each end of the sectionof track over which the highway crosses, distant approach means forregistering the presence of a train on the track adjacent the far end ofeach approach section, each said intermediate approach means including arelay energized by a stick circuit including its own front contact and acontact controlled by the distant approach means and energized by apick-up circuit controlled by the crossing means, said crossing meansincluding a relay normally energized over its front contact or inparallel therewith either both front contacts or both back contacts ofthe relays of the two intermediate approach sections, and circuit meanscontrolled by the crossing means and the intermediate approach means forcontrolling said crossing signal.

2. A control system according to claim 1 wherein the crossing meansincludes directional means for sensing the direction of train movementas Well as the presence of the train in passage through the shortsection of track traversed by the highway, and means controlled by saiddirectional means for further controlling said crossing signal. v i

3. A control system according to claim 1 wherein said distant approachmeans includes a distant approach track circuit having a track relay forregistering the presence of a train.

4. A control system according to claim 1 wherein said relays are trackrelays which are energized in respective track circuits for registeringthe presence of a train.

5. A control system according to claim 1 wherein timing means isprovided for timing an interval after deenergization of said relay ofeither of said intermediate approach means, and circuit means isrendered eflfective by said timing means at the end of said interval forenergizing the relay of said crossing means provided no train 15 isregistered as being present in said short section of track traversed bythe highway.

References Cited in the file of this patent UNITED STATES PATENTS2,027,216 Young 12111.7, 1936

